On 12/6/21 02:15, R.Smith via lazarus wrote:
Firstly the correct way of determinig class (as with your current
solution) is like this:
if (MyObj is TButton) then TButton(MyObj).OnMouseDown := tmethod (not
important here) else
if (MyObj is TPanel) then TPanel(MyObj).OnMouseDown := tmethod (not
important here) else
// etc...
One small detail is that the "is Thing" operator checks if the object
belongs to the class hierarchy introduced by the Thing class, but not
necessarily if it *is* of Thing type - it can be a subclass too.
Sometimes this distinction is important, so in those cases instead of
"is" you can use the ClassType property of objects (e.g. if
MyObj.ClassType=TButton then ...).
(yeah the name of the operator is kinda optimistic in assuming Liskov
substitution principle always applies, but in practice this is often not
the case :-P)
In general assuming two f: TFoo and b: TBar objects with TBar being a
subclass of TFoo, this code:
Writeln(f is TFoo, ' ', b is TFoo, ' ',
f.ClassType=TFoo, ' ', b.ClassType=TFoo);
Will write TRUE TRUE TRUE FALSE (ie, both f and b belong to the class
hierarchy introduced by TFoo but only f is really TFoo and b is not).
Kostas
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